Due to a woman's hips being wider than a mans, in the olden days they were referred to as broads. A tough old broad is an older woman who has seen the hardships throughout history (wars, depressions, the birth of Ryan Seacrest etc) an has kept on keeping on, despite all odds. She can chew up a tin can and spit out fishing hooks if she feels like it.

Check out that tough old broad, she must be like 80 but she just handknitted a shotgun and killed that mugger.